In order to maintain bones in specified orientation relationship, there are various known techniques for screwing a bone-fixing screw into bones in various parts of the body, such as the spine, and combining rods with said implanted screw so that the rods will be positioned alongside the bones. The screws of the prior art are provided with a rod-fixing means. The rod-fixing means have an opening that is located either parallel to the axial direction of thread or on the side thereof, but these solutions have problems; inserted rods slip out of place with the parallel arrangement, while with the latter, operators have to insert a rod at right angles to the axis of the thread, which can prove to be a difficult procedure.